1. Field of the Invention
The present invention relates to an apparatus and method for thermal management of semiconductor devices. More specifically, the present invention relates to a thermal conducting material which provides uniformity and improves thermal dissipation by the integrated circuit.
2. Background of the Invention
In recent years, there has been many advances in integrated circuit technology, especially in semiconductor devices. A semiconductor device is an integrated circuit in packaged form, operating as a processing unit, memory, controller or any other electronic device. The package and packaging techniques currently being used for these semiconductor devices are designed to protect the integrated circuit from damage, to provide electrical connection between the integrated circuit and external electrical devices and, most relevant to the scope of this application, to provide adequate thermal dissipation during operation. These conventional packages include a variety of packages having cavities therein, such as a Ball Grid Array ("BGA"), a Pin Grid Array ("PGA"), a Land Grid Array ("LGA") and other similar packages (hereinafter collectively referred to as a "cavity package").
As shown in FIG. 1, the conventional semiconductor device 1 comprises an integrated circuit die 2, the die 2 being sealed within a cavity 4 of a cavity package 3, such as a PGA package in this embodiment. The cavity package 3 is coupled to a printed circuit board 9 (e.g., a peripheral card, a motherboard and the like) by conventional techniques known in the art to enable the die 2 to operate within the computer system. The die 2 is bordered along its perimeter by a plurality of cavity side walls such that side walls 4a and 4b border opposite sides of the die 2. The die 2 is further bordered along a top portion 3b of the package cavity 3 by a package lid 5. In accordance with industry standards, the top portion 3b of the cavity package 3 is that surface directly opposite the printed circuit board 9 when the semiconductor device 1 is coupled thereto and a bottom portion 3a is that surface furthest away from the printed circuit board 9.
During operation, the die 2 consumes power and generates heat as a byproduct. Unfortunately, the die 2 does not generate heat in a uniform manner along its surface. Rather, the die 2 typically has a surface temperature varying from one location to another by as much as 25.degree. Celsius. The locations having these higher temperatures, referred to as "hot spots", which decrease die reliability and reduce the useful life of the die 2 by accelerating time-temperature failure mechanisms (i.e., increasing transistor leakage) at the hot spots over what they would be at a lower, average temperature for the entire die. Moreover, these hot spots cause otherwise identical devices to exhibit different operating parameters and to age differently because of the different temperatures thereof, thereby raising the probability of early and unpredictable out of operating range device parameters for the integrated circuit in question. Attempts to reduce the number of hot spots have been directed to minimizing current density per unit area of the die 2 as well as providing reliable thermal dissipation.
Typically, for lower power consumption semiconductor devices as shown in FIG. 1, thermal dissipation is be accomplished by transferring the heat from the die 2, through a heat conductive gaseous medium (e.g., air) within the cavity 4, to the cavity package 3. Thereafter, the cavity package 3 dissipates the heat to an atmosphere surrounding the cavity package 3. However, for higher power consumption semiconductor devices, the cavity package 3 is incapable of providing adequate thermal dissipation by itself.
Referring to FIG. 2, a conventional thermal transfer device 6 to be embedded into the bottom portion 3a of the cavity package 3 proximate to the die 2 is shown. Currently, the most cost-effective thermal transfer device 6 is a heat slug 7 in combination with a larger heat sink 8. The heat slug 7 is molded proximate to the die 2 in the bottom portion 3a of the chip package 3 in order to conduct heat from the die 2. Since the heat slug 7 has negligible surface area exposed to the surrounding atmosphere, not suitable for optimal thermal dissipation, the heat sink 8 is commonly mounted onto the heat slug 7 for thermal dissipation purposes.
Recently, technological advances in the semiconductor industry have led to "improved" semiconductor devices which have larger chip sizes and operate at higher clock frequencies. As a result, these improved semiconductor devices consume more power than previous generation semiconductor devices, and therefore, require greater thermal dissipation to operate at a desired temperature. It is now being discovered that the heat slug 7 and heat sink 8 is incapable of providing adequate thermal dissipation to many improved semiconductor devices. Thus, the semiconductor industry is being forced to adopt more expensive alternative thermal transfer devices, resulting in a more costly final product for the consumer.
Hence, it would be desirable to develop an apparatus and method for enhancing thermal dissipation so as to eliminate the need for a heat slug/sink combination in some cases, and especially costly alternative thermal transfer devices.